With a known method of this kind (Technische Information NM 142/01 (Technical Information) by Messrs. Netzsch-Mohnopumpen GmbH, D-8264 Waldkraiburg) the speed of the filling pump and thus the quantity being fed is reduced in steps when a predetermined filtration pressure has been reached. When a predetermined minimum speed has been reached, the filling pump is turned off by an end switch. After turn off of the filling pump only the high pressure pump remains in operation for the remainder of the charging time, and it increases the charging pressure to the final pressure. As there is no harmonized utilization of the performances of the two pumps connected in parallel, the charging time is long and, therefore, the operating costs are high.
Likewise known is a method of feeding material to a filtering apparatus by means of a feed pump (EP-A-No. 0 027 910) with which the feeding is effected in repeated press cycles during the course of which the feed pump is operating which is rendered idle upon reaching of a predetermined limit value of the pressure in the respective feeding or charging phase until the feeding or charging pressure has again dropped to a lower limit value. The operating behaviour is uneconomical as the feed pump is being switched on and off.